Invasive species reshaping Guam island's forests

Guam, a lush emerald island in the western Pacific, faces a unique ecological crisis.

Guam is home to 40 times more spiders than its neighboring islands, along with a population of invasive snakes so ravenous that they have eradicated all the birds from the forests.

Five years ago, Haldre Rogers found himself at a gathering on the island of Guam, a lush green spot in the western Pacific Ocean, about 2,492 km (1,548 miles) from the Philippines. The festivities took an unexpected turn when an uninvited guest appeared.

It was late in the evening, and a hog was roasting outside, the remnants of dinner. The fire was dying down but still warm. As guests momentarily stepped away to mingle, they returned to find a brown shape coiled around the pig—a shiny, scaly creature with vertical slit-eyes and a wide, grinning mouth. This creature was tearing into the pig's flesh and gulping it down whole, slowly ingesting it into its swollen body.

"It wasn't [exactly] a 400-pound (181kg) pig, but it was a pig for a big party," says Rogers, an associate professor in the Department of Fish and Wildlife Conservation at Virginia Tech in the US, who has been researching Guam's ecology for the past 22 years.

The unwelcome guest was a brown tree snake—an invasive species believed to have accidentally arrived in Guam in the 1940s, possibly by hiding on a cargo ship. Prior to this invasion, a wealth of native birds thrived in the island's unique limestone forests. However, within just four decades of the snake's introduction, these insatiable predators had stripped the jungle of every bird. Out of 12 species, 10 are now extinct, with the remaining two barely surviving in remote caves and urban areas.

With the avian population nearly eradicated, Guam's estimated two million snakes—an uncertain count—will consume anything they can find, including rats, shrews, lizards, or, in this instance, human leftovers.

"I mean, they'll eat anything," says Henry Pollock, executive director of the Southern Plains Land Trust, a non-profit organization in Colorado that has studied Guam's ecology. "They'll eat each other."

Amid this infestation of voracious snakes and the absence of the cheerful sounds of birds, Guam has become infamous for one of the most significant ecological disasters on the planet. The impact of the snake invasion reaches far beyond the eerily quiet forests. Here, an evolutionary experiment is taking place, with one notable beneficiary possessing eight legs and numerous eyes, fortunate to inhabit an island where sharp, hungry beaks are merely a distant memory.

Rogers isn’t afraid of spiders—and that's fortunate. On most of the Mariana Islands, spider populations are relatively low during the rainy season, with a significant increase as the weather dries. However, Guam is different. The island's limestone forests are an arachnid nightmare year-round, featuring an almost continuous web of silvery strands that stretches for miles, revealing new webs and their hairy occupants with every step.

By Naila Huseynova